A combinatorial approach toward fabrication of surface-adsorbed metal nanoparticles for investigation of an enzyme reaction.

We are presenting a combinatorial approach for the preparation of surface-adsorbed metal nanoparticles for investigation of biological phenomena. Metal nanoparticles, in particular noble metal nanoparticles, have become increasingly recognized for their importance in studies of biological systems. An intense near-field associated with these particles can be exploited to improve the performance of various spectroscopic techniques. In this paper, we combine the metal nanoparticle with a colorimetric enzyme reaction and explore spectral changes of the metal nanoparticle dependent on the extent of the reaction, alkaline phosphatase acting on nitro-blue tetrazolium chloride. Changing the shape of the gold particle has a clear effect on the extent of the spectral shift. Furthermore, we demonstrate that the method we employ for preparation of metal particles, vacuum evaporation of a metal on a monolayer of surface-adsorbed monodisperse polystyrene or silica nanospheres, is supremely suited for a combinatorial approach. By depositing two different metals on nanospheres as multi-layers while varying the ratio as well as absolute thicknesses, it is possible to produce a large variety of metal particles in parallel. We show the potential of such a combinatorial approach for rapidly producing metal nanoparticles of choice.